No lamp can use the entire absorbed energy for radiating light. LED lamps are, of course, much more efficient than the traditional halogen– or xenon lamps, but even with them, there are various losses that must be taken into consideration. 

Thermal losses: LEDs have the property of producing less and less light with increasing operating temperature. But like any electrically driven component, LEDs also heat up in operation. In actuality, it is not unusual for LEDs, for example, to reach temperatures in excess of 100 °C during operation. Thus, it is logical that the light output of an LED that has just been switched on and is still cool is higher than that of another LED that is already glowing for 30 minutes. 

Losses from applied voltage: The higher the operating voltage of the installed LEDs is, the more light they will produce. But the thermal load also increases to the same extent; as mentioned above, the thermal load in turn results in a reduced light yield. In this manner, an increase in the operating voltage can result in a reduction in the relative light output and shortening of the service life of the LEDs. 

Other losses: Other essential factors that influence the light output are the so-called optical losses and the differences in the construction of the overall light. Whenever light has to pass through a substance or is reflected by a substance, it loses a part of its intensity. The losses of every light will depend on its lens (and/or diffusion disc) or the reflector. If these points are now combined with other differences in the construction, then as a guide value, we get a loss of 20-50 percent, which is not taken into account simply by specifying the theoretically possible output of a lamp.

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